This invention relates to a process for the preparation of acetals of 2-haloaldehydes, or 2-haloaldehyde acetals or simply 2-haloacetals, by subjecting primary alcohols having at least one beta-hydrogen atom to electrolysis under substantially anhydrous conditions in the presence of anhydrous hydrogen halide selected from the group consisting of hydrogen chloride and hydrogen bromide in an electrolytic cell. Exemplary of the 2-haloaldehyde acetals is chloroacetal (chloroacetaldehyde diethyl acetal) prepared from absolute ethanol and anhydrous hydrogen chloride. The products are useful as versatile bifunctional reagents. They can react either as alkyl halides or as sources of the aldehyde functionality, or both.
The preparation of acetals of 2-haloaldehydes, particularly acetals of 2-chloroaldehydes has been previously described in the prior art. Bievre et al, Bulletin des Societes Chimiques Belges, 68, 550-557 (1959) describes the preparation of chloroacetaldehyde diethyl acetal by treating ethyl alcohol with chlorine gas. Chattaway et al, Journal of the Chemical Society, 125, 1097-1101 (1924); Fritsch, Annalen, 279, 288-300 (1894); and Lieben, Annalen, 104, 114-115 (1857) describes similar procedures. Overall, the reaction proceeds according to diagrammatically simplified reaction (1). EQU 3CH.sub.3 CH.sub.2 OH + 2Cl.sub.2 .fwdarw. ClCH.sub.2 CH(OCH.sub.2 CH.sub.3).sub.2 + 3HCl + H.sub.2 O (1)
However, chemical routes involving these raw materials suffer from the disadvantage that the reaction produces three moles of hydrogen chloride per mole of acetal. The disposal of this large volume of hydrogen chloride presents obvious difficulties which significantly detract from the attractiveness of such chemical processes for large scale reactions.
It has now been discovered tha the difficulties and disadvantages associated with the prior art chemical processes are overcome by the process of the present invention which represents a substantial improvement in the sense that
(A) HYDROGEN HALIDE IS CONSUMED DURING THE REACTION, THEREBY ALLEVIATING THE PROBLEM OF DISPOSAL OF LARGE VOLUMES OF HYDROGEN HALIDE; AND
(B) ONLY INNOCUOUS CO-PRODUCTS--HYDROGEN, WHICH MAY BE BURNED TO WATER, AND WATER ITSELF--ARE PRODUCED DURING THE REACTION.
Various other advantages of this invention will become apparent from the accompanying description and claims.